Escalators are provided with safety systems, each one of which is operable to stop movement of the escalator in the event that an unsafe operating condition is detected. Examples of such unsafe operating conditions include: a missing step or a detached step on the escalator; a handrail which is moving at an improper speed; something becoming caught between adjacent steps or between the steps and the side skirts; a foreign object becoming lodged between the step treads and the comb plate at the escalator exit landing; or the like. The safety system components used to detect unsafe escalator operating conditions include proximity sensors, switches, pressure sensors, or the like, which are able to detect unsafe escalator-operating conditions so long as the sensors and their associated circuitry remain operative.
U.S. Pat. No. 5,601,178 describes a method and apparatus for checking escalator safety circuit components to confirm circuit operability prior to start up of motion of the escalator. A start up check relay is energized whenever escalator motor motive power is interrupted. The start up check relay checks speed and non-speed-dependent safety circuit components to determine whether these safety circuit components have all come to an escalator start up state. When the start up condition of these safety circuit components has been verified the circuit allows power to be applied to the escalator motor. When power is applied to the escalator motor, a start up delay timer is energized and the start up check relay is de-energized. When speed-dependent components of the escalator have come to operating speeds, the start up delay timer will be de-energized, and the escalator will continue movement in its normal operating mode provided that all safety circuits are fully operational.
U.S. Pat. No. 6,230,871 describes a device for monitoring functional units on escalators and moving walkways, comprising several processors which monitor predetermined parameters of a particular functional unit independently of each other. The processors are connected to devices for immediately shutting down the escalator or moving walkway and interact with at least one other processor which is provided for controlling and/or diagnosing functions which are not relevant to safety.
U.S. Pat. No. 6,758,319 describes a method and a system for disconnecting passenger transport systems, especially escalators and moving walkways. Functional units of a passenger transport system monitor for malfunctions of the passenger transport systems by using switching elements and the signals of the functional units are combined to form a security chain. The signals of the functional units and signals from a drive monitoring unit are supplied to at least one pilot unit. Subsequently, a disconnecting signal is provided to a respective disconnecting contact as a result of a malfunction detected by the functional units and/or the drive monitoring system.
Current safety systems require large amounts of wiring and switches. Also, there is no mechanism provided for determining the operability of the safety system detectors or their circuitry. There is a need for a cost effective solution that addresses these problems.